1. Field of the Invention
The present invention relates to a backhoe hydraulic system in which a swivel base equipped with a ground working device is mounted so as to be able to swivel on a travel body about a vertically directed central axis.
2. Description of the Related Art
Conventional backhoe hydraulic systems in which a swivel base equipped with a hydraulically driven ground working device is mounted so as to be able to swivel on a travel body provided with a pair of hydraulically driven left and right travel devices about a vertically directed central axis include a system that is configured so that during a non-travel state, pressure oil from a first pump and a second pump is fed together to the ground working device, and the pressure oil from a third pump is fed to a swivel motor for swiveling the swivel base. During a travel state, the pressure oil from the first pump is fed to one of the left and right travel devices, the pressure oil from the second pump is independently fed to the other of the left and right travel devices, and the pressure oil from the third pump is fed to a hydraulic actuator of the ground working device (see JP 2006-161510A, for example).
This hydraulic system is provided with a first flow channel switching valve that is capable of switching between a work position in which pressure oil from the first pump and the second pump is fed together to a control valve for the ground working device, and a travel position in which the pressure oil from the first pump and the second pump is fed independently to a control valve for the left and right travel devices; and a second flow channel switching valve that is capable of switching between a non-feeding position in which the pressure oil from the third pump is not fed to the control valve for the ground working device, and a feeding position in which the pressure oil from the third pump is fed to the control valve for the ground working device.
In the hydraulic system, the second flow channel switching valve and the first flow channel switching valve are composed of pilot-operated switching valves that are switched by a pilot pressure, and are configured so that the pilot pressure is fed to a travel-independent valve and the flow channel switching valves when operation of the control valve for the travel device is detected, and the pilot pressure is fed to the flow channel switching valves when operation of the control valve for the ground working device is detected.
The first flow channel switching valve is also configured so as to by switched from the work position to the travel position by the pilot pressure that is created by the operation of the control valve for the travel device, and the second flow channel switching valve is configured so as to remain in the non-feeding position without being switched to the feeding position by the pilot pressure created by the operation of the control valve for the ground working device during the non-travel state, and to by switched to the feeding position by the pilot pressure that is the sum of the pilot pressure created by the operation of the control valve for the travel device, and the pilot pressure created by the operation of the control valve for the ground working device when the ground working device is in use, and the control valve for the travel device is operated.